3D variable resistance memory device having junction FET and driving method thereof

ABSTRACT

A 3D variable resistance memory device having a junction FET and a driving method thereof are provided. The variable resistance memory device includes a semiconductor substrate and a string selection switch formed on the semiconductor substrate. A channel layer is formed on the column string selection switch. A plurality of gates stacked along a length of the channel layer and each of the gates contacts an outer side of the channel layer. A variable resistance layer is formed on an inner side of the channel layer, and contacts the channel layer.

CROSS-REFERENCES TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.13/949,529 filed on Jul. 24, 2013, which claims priority under 35 U.S.C.119(a) to Korean application number 10-2013-0038587, filed on Apr. 9,2013, in the Korean Patent Offices. The disclosure of each of theforegoing applications is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The inventive concept relates to a semiconductor integrated circuitdevice, and more particularly, to a three-dimensional (3D) variableresistance memory device having a junction FET, and a driving methodthereof.

2. Related Art

With the rapid development of mobile and digital informationcommunication and consumer-electronic industry, studies on existingelectronic charge controlled-devices are expected to encounter thelimitation of the studies. Thus, new functional memory devices need tobe developed. In particular, next-generation memory devices with largecapacity, ultra-high speed, and ultra-low power need to be developed.

Currently, resistive memory devices using a resistance device as amemory medium have been suggested as the next-generation memory devices.Typically, phase-change random access memories (PCRAMs), resistance RAMs(ReRAMs), and magentoresistive RAMs (MRAMs) are used as the resistivememory devices.

The resistive memory devices may be basically configured of a switchingdevice and a resistance device and store data “0” or “1” according to astate of the resistance device.

Even in the resistive memory devices, the first priority is to improveintegration density and to integrate memory cells in a narrow area asmany as possible. Further, when a plurality of memory cells areintegrated in a limited region, switching performance has to be ensured.

SUMMARY

One or more exemplary implementations are provided to a 3D variableresistance memory device capable of improving integration density andensuring switching performance, and a driving method thereof.

An exemplary variable resistance memory device may include asemiconductor substrate; a string selection switch formed on thesemiconductor substrate; a channel layer formed on the column stringselection switch; a plurality of gates stacked along a length of thechannel layer, wherein each of the gates contacts an outer side of thechannel layer; and a variable resistance layer formed on an inner sideof the channel layer, wherein the variable resistance layer contacts thechannel layer.

An exemplary variable resistance memory device may include a commonsource line; a plurality of strings of memory cells electricallyconnected, in series, to the common source line; a bit line electricallyconnected to the plurality of strings of memory cells; and a pluralityof column string selection switches, each electrically connected to acorresponding one of the plurality of strings of memory cells, whereineach of the memory cells includes a variable resistance layer, and ajunction transistor configured to selectively provide current to thevariable resistance layer.

A method of driving an exemplary variable resistance memory device, inwhich a plurality of memory cells are stacked, and each of the pluralityof memory cell includes a junction transistor and a variable resistorconnected in parallel to the junction transistor, the method comprisingturning off a junction transistor of a selected one of the plurality ofstacked memory cells; and turning on junction transistors ofnon-selected memory cells of the plurality of stacked memory cells toform a current path in a variable resistance layer of the selectedmemory cell.

These and other features, aspects, and implementations are describedbelow in the section entitled “DETAILED DESCRIPTION”.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thesubject matter of the present disclosure will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a circuit diagram illustrating an exemplary variableresistance memory device;

FIG. 2 is a circuit diagram illustrating an exemplary;

FIGS. 3 to 5 are cross-sectional views illustrating driving of anexemplary junction transistor;

FIG. 6 is a circuit diagram illustrating a driving method of anexemplary variable resistance memory device; and

FIGS. 7 to 11 are cross-sectional views sequentially illustrating amethod of manufacturing an exemplary variable resistance memory device.

DETAILED DESCRIPTION

Hereinafter, exemplary implementations will be described in greaterdetail with reference to the accompanying drawings.

Exemplary implementations are described herein with reference tocross-sectional illustrations that are schematic illustrations ofexemplary implementations (and intermediate structures). As such,variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, exemplary implementations should not be construed aslimited to the particular shapes of regions illustrated herein but maybe to include deviations in shapes that result, for example, frommanufacturing. In the drawings, lengths and sizes of layers and regionsmay be exaggerated for clarity. Like reference numerals in the drawingsdenote like elements. It is also understood that when a layer isreferred to as being “on” another layer or substrate, it can be directlyon the other or substrate, or intervening layers may also be present.

Referring to FIG. 1, a variable resistance memory device 10 includes aplurality of memory cells mc1, mc2, mc3, and mc4 connected in series.

The plurality of memory cells mc1, mc2, mc3, and mc4 connected in seriesmay be connected between a bit line BL and a common source line CS. Thatis, the plurality of memory cells mc1, mc2, mc3, and mc4 connected inseries may be implemented by sequentially stacking the memory cells mc1,mc2, mc3, and mc4 on a semiconductor substrate (not shown). In theexemplary implementation, the stacked memory cells mc1 to mc4 connectedin series may be connected to one bit line BL, and may be referred to asa column string SS1 and SS2. A plurality of column strings SS1 and SS2may be connected to one bit line BL.

Each of the plurality of memory cells mc1 to mc4 may include a switchingdevice SW1 to SW4 and a variable resistor R1 to R4, and the switchingdevice SW1 to SW4 and the variable resistor R1 to R4 constituting eachmemory cell mc1 to mc4 may be connected in parallel to each other.

As the switching devices SW1 to SW4, a junction field effect transistor(FET) may be used. The variable resistors R1 to R4 may include variousmaterials, such as a PrCaMnO (PCMO, Afterward use abbreviation.) layerfor a ReRAM, a chalcogenide layer for a PCRAM, a magnetic layer for aMRAM, a magnetization reversal device layer for a spin-transfer torquemagnetoresistive RAM (STTMRAM), or a polymer layer for a polymer RAM(PoRAM).

A column switch array 15 may be connected between the column strings SS1and SS2 and the common source line CS. The column switch array 15 mayinclude a plurality of string selection switches SSW1 and SSW2. Thestring selection switches SSW1 and SSW2 may be connected to the columnstrings SS1 and SS2 one by one, and each of the string selectionswitches SSW1 and SSW2 may selectively connect a corresponding columnstring SS1 or SS2 and the common source line CS in response to acorresponding selection signal a1 or a2.

Alternatively, the column switch array 15 may be arranged between thecolumn strings SS1 and SS2 and the bit line BL as illustrated in FIG. 2.The same effect as in the variable resistance memory device of FIG. 1may be obtained.

A junction FET may be used as the switching devices SW1 to SW4 in anexemplary implementation. In the function FET, an area of a depletionlayer is changed according to a gate bias, and a switching operation isperformed.

Referring to FIG. 3, a source 25 a and a drain 25 b are formed in bothends of a channel layer 20. A gate 30 is formed around the channel layer20 without a gate insulating layer interposed therebetween. The channellayer 20 may include an N-type impurity. The source 25 a and the drain25 b may include a high concentration of the N-type impurity. The gate30 may be a semiconductor layer including a high concentration of aP-type impurity. A depletion layer 35 may be formed between the gate 30and the channel layer 20 and may form by a junction region between thegate 30 and the channel layer 20.

FIG. 3 shows a state in which no voltage is applied to the gate 30, thesource 25 a, and the drain 25 b in the junction FET.

FIG. 4 shows a state in which the junction FET is turned on. In thisstate, a voltage +V is applied to the drain 25 b and the depletion layer35 is expanded to flow current in the channel layer 20.

FIG. 5 shows a state in which 0 (zero) voltage is applied to the source25 a, and a positive voltage +V is applied to the drain 25 b. If areverse bias voltage −V is applied to the gate 30, then an area of thedepletion layer 35 is increased and closes the channel layer 20.Therefore, the junction FET is turned off.

Thus, the junction FET used for the switching devices SW1 to SW4 mayperform switching of the variable resistance memory device throughcontrol of the area of the depletion layer by the gate bias.

Hereinafter, the operation of the variable resistance memory deviceaccording to an exemplary implementation will be described.

In the exemplary implementation, a process of reading and writing datafrom and to a third memory cell mc3 of a first column string SS1 will bedescribed.

Referring to FIG. 6, a high voltage is applied to a gate a1 of a firststring switch SSW1 to select the first column string SS1.

To write data to the third memory cell mc3, in a state in which ajunction FET of the third memory device mc3 is turned off (see FIG. 6),junction FETs of first, second, and fourth memory cells mc1, mc2, and,c4 are floating or turned on (see FIG. 4 or 5).

That is, 0 (zero) voltage or a positive voltage +V is applied to thefirst, second, and fourth junction FETs SW1, SW2, and SW4, and anegative voltage −V is applied to a gate of a third junction FET SW3.

Accordingly, the fourth, second, first junction FETs SW4, SW2, and SW1in the fourth, second, and first memory cells mc4, mc2, and mc1 areturned on, and a current path is formed in the junction FETs SW4, SW2,and SWL. On the other hand, the third junction FET SW3 in the thirdmemory cell mc3 is turned off, and a current path is formed in a thirdvariable resistor R3.

Therefore, a write current Iw provided from the bit line BL flows to thecommon source line CS through the fourth junction FET SW4, the thirdvariable resistor R3, and the second and first junction transistors SW2and SW1. Therefore, data is written in the third variable resistor R3during the process.

In the same state as in the above-described write operation, a readcurrent Ir is provided from the bit line BL. The read current Ir reachesthe common source line CS connected to a ground through a correspondingcurrent path. The data written in the variable resistor R3 may bechecked by measuring a current value reaching the common source line CS.At this time, the read current Ir has a level that does not affect adetermination of a state of the variable resistor R3, and may have alower value than the write current Iw.

FIGS. 7 to 11 are cross-sectional views illustrating a process ofmanufacturing an exemplary variable resistance memory device.

Referring to FIG. 7, a common source region 105 is formed on asemiconductor substrate 100. The common source region 105 may include,for example, an impurity region or a conductive layer. A common sourceregion 105 including an impurity region may be formed by implanting animpurity having a conductivity type opposite a conductivity type of thesemiconductor substrate. For example, the common source region 105 mayinclude an N-type impurity formed in a P-type semiconductor substrate100. Alternatively, a common source region 105, including a conductivelayer, may be formed by depositing a polysilicon layer on thesemiconductor substrate 100.

A conductive layer may be formed on the common source region 105 andthen patterned to form a pillar 110 for formation of a channel of astring selection switch. For example, the conductive layer for thepillar may include a semiconductor layer such as a polysilicon layer. Adrain region 115 may be formed by implanting an impurity, having thesame conductivity type as the impurity of the common source region 105,into an upper portion of the pillar 100. Therefore, a channel formationregion is defined in the pillar 110. At this time, the pillar 110 may beformed in regions defined as the column strings SS1 and SS2.

A gate insulating layer 120 may be deposited on the semiconductorsubstrate 100 in which the pillar 110 is formed, and a gate 125 may beformed to surround the pillar 110. Therefore, the string selectionswitches SSW1 and SSW2 having a vertical structure are completed.

An interlayer insulating layer 130 may be formed to cover thesemiconductor substrate 100 in which the string selection switches SSW1and SSW2 are formed. The interlayer insulating layer 130 may be formedto have a thickness sufficient to bury the string selection switchesSSW1 and SSW2. The Interlayer insulating layer 130 may be planarized toexpose the drain region 115. An ohmic layer 135 may be formed in theexposed drain region 115 through a general process. In an exemplaryimplementation, a silicide layer may be used as the ohmic layer 135, forexample.

Referring to FIG. 8, insulating layers 140 a, 140 b, 140 c, 140 d, and140 e and conductive layers 145 a, 145 b, 145 c, and 145 d arealternately deposited on the interlayer insulating layer 130 to form astacked gate structure. The insulating layer 140 e may be located in theuppermost layer of the stacked gate structure. In an exemplaryimplementation, four conductive layers 145 a, 145 b, 145 c, and 145 dmay be alternately stacked with the insulating layers 140 a, 140 b, 140c, and 140 d, so that four memory cells are stacked. Therefore, a memorycell is a stack of a conductive layer and an insulating layer.

The conductive layers 145 a, 145 b, 145 c, and 145 d may be a materialfor a gate of the junction FET constituting the memory cell. Forexample, the material for the gate of the junction FET may includetungsten (W), copper (Cu), titanium nitride (TiN), tantalum nitride(TaN), tungsten nitride (WN), molybdenum nitride (MoN), niobium nitride(NbN), titanium silicon nitride (TiSiN), titanium aluminum nitride(TiAlN), titanium boron nitride (TiBN), zirconium silicon nitride(ZrSiN), tungsten silicon nitride (WSiN), tungsten boron nitride (WBN),zirconium aluminum nitride (ZrAlN), molybdenum silicon nitride (MoSiN),molybdenum aluminum nitride (MoAlN), tantalum silicon nitride (TaSiN),tantalum aluminum nitride (TaAlN), titanium (Ti), molybdenum (Mo),tantalum (Ta), titanium silicide (TiSi), tantalum silicide (TaSi),titanium tungsten (TiW), titanium oxynitride (TiON), titanium aluminumoxynitride (TiAlON), tungsten oxynitride (WON), or tantalum oxynitride(TaON). In an exemplary implementation, if the gate conductive layers145 a, 145 b, 145 c, and 145 d include a metal material, then an ohmiccontact layer may be formed in a contact portion with the channel layerto be formed later.

Referring to FIG. 9, the insulating layers 140 a, 140 b, 140 c, 140 d,and 140 e and the conductive layers 145 a, 145 b, 145 c, and 145 d areetched to form a hole H exposing the ohmic layer 135 on the pillar 110.

Referring to FIG. 10, a channel layer 155 of the junction FET and avariable resistance layer 160 are sequentially formed on along the innersurface of the hole H. The channel layer 155 and the variable resistancelayer 160 may be conformally formed to a uniform thickness. Since thechannel layer 155 is formed along the surface of the insulating layers140 a, 140 b, 140 c, 140 d, and 140 e and the conductive layers 145 a,145 b, 145 c, and 145 d that define the hole H, the channel layer of thejunction FET may be formed perpendicular to a surface of the substrate.In an exemplary implementation, the channel layer 155 may be an N-typesemiconductor layer, such as a silicon (Si) layer, a silicon germanium(SiGe) layer, or a gallium arsenide (GaAs) layer. The variableresistance layer 160 may include various materials, such as a PCMOlayer, which is a material for a ReRAM, a chalcogenide layer, which is amaterial for a PCRAM, a magnetic layer, which is a material for a MRAM,a magnetization reversal device layer, which is a material for aspin-transfer torque magnetoresistive RAM (STTMRAM), or a polymer layer,which is a material for a polymer RAM (PoRAM). A buried insulating layer165 is formed in the hole H in which the channel layer 155 and thevariable resistance layer 160 are formed. In an alternative exemplaryimplementation, the buried insulating layer 165 may be omitted byincreasing the thickness of the variable resistance layer 160.

Referring to FIG. 11, a bit line 170 is formed, via a known method, onthe insulating layers 140 a, 140 b, 140 c, 140 d, and 140 e, theconductive layers 145 a, 145 b, 145 c, and 145 d, and the buriedinsulating layer 165. Before the forming of the bit line 170, additionalinsulating material may be formed in the conductive layers 145 a, 145 b,145 c, and 145 d between the holes H, so that the bit line may beimplemented in the same shape as the gate of the string selectionswitch.

The 3D variable resistance memory device may perform data read and writeby forming a current path in a variable resistor of the selected memorycell through application of the reverse bias to the cell gate asdescribed with reference to FIGS. 3 to 5. In an exemplaryimplementation, a plurality of memory cells are formed in a limitedspace in a stacking manner through the stacking of the cell gates, andthus integration density may be improved. Further, the junction FET withthe simplified structure and good switching performance is used as aswitching device and thus switching characteristics and structuralstabilization may be obtained.

The above description is illustrative and not limitative. Variousalternatives and equivalents are possible. The invention is not limitedby the exemplary implementation described herein. Nor is the inventionlimited to any specific type of semiconductor device.

What is claimed is:
 1. A method of driving a variable resistance memorydevice, in which a plurality of memory cells are stacked, and each ofthe plurality of memory cell includes a junction transistor and avariable resistor connected in parallel to the junction transistor, themethod comprising: turning off a junction transistor of a selected oneof the plurality of stacked memory cells; and turning on junctiontransistors of non-selected memory cells of the plurality of stackedmemory cells to form a current path in a variable resistance layer ofthe selected memory cell.